The present invention relates to transparent bar soaps, and more particularly to moisturizing transparent bar soaps essentially free of monohydric alcohol and having a high humectant content.
A personal bar soap is characterized as "moisturizing" if the bar soap contains an agent that helps retain moisture in the skin (i.e., a "humectant"). Humectants (such as glycerin) help prevent the skin from excessively drying during the wash process. Excessive skin drying can result in raw, red, chapped, irritated, itchy, or cracked skin--especially for those with sensitive skin or during the winter months when indoor air heating can create very dry air that contributes to skin drying. Generally, the more humectant that is present in the bar soap, the better the moisturizing attributes of the soap.
Consumers consider a transparent bar soap having a high humectant content as a premium bar soap, not only because of the enhanced moisturizing properties, but also because the humectant content significantly increases the cost of the bar soap. However, increasing the amount of glycerin humectant to provide better moisturization for a transparent bar soap generally decreases the desirable hardness, resistance-to-wear, and foaming attributes of the bar. For example, U.S. Pat. No. 5,786,311 issued Jul. 28, 1998 to Zyngier entitled "Monohydric Alcohol-Free Process for Making a Transparent Pour Molded Personal Cleansing Bar" states that the amount of humectant (such as glycerin and propylene glycol) in the transparent bar soap should not exceed about 37%. (Column 7, lines 6-9.) Further, although the hardness and detergency of a bar soap can be improved by increasing the fatty acid soap content, that component also tends to negatively affect the transparency of the bar soap.
Soap formulators have addressed these problems by adding significant amounts of monohydric alcohol (e.g., ethanol) to dissolve the fatty acid soap. However, monohydric alcohols contribute to skin dryness. Also, bars containing monohydric alcohol typically display increased weight loss due to evaporation of the volatile alcohol. Specialized and expensive explosion-proof process equipment is also required with monohydric alcohol-containing soap formulations, due to the volatile and explosive nature of monohydric alcohols.
The fatty acid soap component of a bar soap can be made in situ by the well-known saponification process--that is, the reaction of triglyceride with caustic to produce fatty acid soap and glycerin. However, the high temperature associated with the saponification process frequently causes undesirable discoloration of soap bars.